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.\"     @(#)sleep.3	8.1.1 (2.11BSD) 1997/9/26
.\"
.TH SLEEP 3 "September 26,1997"
.UC 3
.SH NAME
\fBsleep\fP, usleep \- suspend process execution
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.nf
unsigned int
sleep(seconds)
      unsigned int seconds;
.sp
void
usleep(microseconds)
       long microseconds;
.fi
.SH DESCRIPTION
The
.B sleep
function suspends execution of the calling process for
.I seconds
of clock time, or until interrupted by a signal.
.PP
The
.B usleep
function suspends execution of the calling process for
.I microseconds
of clock time, or until interrupted by a signal.
.PP
System activity may lengthen the suspension.
.SH RETURN VALUES
The
.B sleep
function returns 0, or if interrupted before
.IR seconds,
the amount not slept (the requested time minus the time actually slept)
in seconds.  The
.B usleep
function does not return anything (meaningful).
.SH SEE ALSO
select(2)
.SH COMPATIBILITY
Previous implementations of
.B sleep
and
.B usleep
re-suspended the process if interrupted by a signal.
This implementation has been changed to return in that case,
to conform to POSIX 1003.1-88.
.PP
On the PDP-11 the previous version of \fBusleep\fP took a \fIu_int\fP as 
the input parameter.  This has been changed to be \fIlong\fP so that
\fBusleep\fP can be used for more than 65 milliseconds (a u_int could only
count 65535 microseconds) of sleep.  Thus it is now possible for 
\fBusleep\fP to handle longer sleep durations than \fBsleep\fP.
.SH BUGS
On the PDP-11 the clock resolution is limited to the line frequency (usually
60Hz in the U.S.A. and 50Hz elsewhere).
.SH HISTORY
A
.B usleep
function appeared in
4.3BSD.
A
.B sleep
function appeared in V7.
